A Management Data Input/Output (MDIO) interface is a serial bus defined as part of the IEEE 802.3 standard related to wired Ethernet devices. An MDIO interface is also known as a Serial Management Interface (SMI) or a Media Independent Interface Management (MIIM). MDIO interfaces are routinely used to transport data between different devices over serial data connections.
Physical layer (PHY) management interfaces often use an Ethernet bus so that a media access control (MAC) device (such as master device) can read and write control and status registers of one or more devices connected to the bus. PHY management interfaces also often use an Ethernet bus so that a MAC device can read and write control status registers of Ethernet switches, which are used to configure the PHY devices and Ethernet switches before operation. In addition, PHY management interfaces often use an Ethernet bus so that a MAC device can monitor link status during operation.